Turbine engine lubrication method and system

ABSTRACT

A method and a system for lubricating a turbomachine including an oil tank, an oil feed pump, an oil/air separator, and at least two enclosures closed by air flow rate seals, each including a low outlet and housing shaft-supporting rolling bearings. The method injects oil from the tank into the enclosures by the pump to lubricate the bearings, introduces compressed air at a low flow rate into the enclosures via the seals to pressurize the enclosures, recuperates all of the air and the oil introduced into the enclosures via their low outlet, uses gravity and the pressurization of the enclosures to convey the oil/air mixture as recovered in this way to the oil/air separator, separates the oil and the air of the mixture by the oil/air separator, returns the oil to the tank, and exhausts the air to outside the turbomachine.

BACKGROUND OF THE INVENTION

The present invention relates to the general field of lubricating anaviation turbomachine.

An aviation turbomachine has numerous elements that need to belubricated; these include in particular rolling bearings used forsupporting the rotary shafts, and also the gearing, of the accessorydrive gearbox.

In order to reduce friction, wear, and heating due to the high speed ofrotation of the turbomachine shafts, the bearings that support them needto be lubricated. Since providing lubrication merely by injecting oilduring maintenance of the turbomachine is not sufficient, use isgenerally made of so-called “dynamic” lubrication.

Dynamic lubrication consists in causing oil to circulate continuously ina lubrication circuit. A flow of lubricating oil from a tank is thusdelivered to the bearings by a pump, which bearings are housed inenclosures that are closed by seals. In order to avoid lubricating oilleaking from the enclosures to the remainder of the turbomachine via theseals, a flow of air is taken from one of the compressors of theturbomachine and is injected through the seals. The enclosures are thuspressurized at a pressure higher than atmospheric pressure.

The major fraction of the air introduced into the enclosures is thenexhausted to the outside of the turbomachine by following a specialcircuit designed to de-oil the air and to control the pressure insidethe enclosures. The lubricating oil injected into the enclosures isrecovered from the bottoms thereof by recovery pumps via another specialcircuit. In order to ensure that the enclosure is completely dry, asmall fraction of the air is also sucked out by these pumps and theoil/air mixture as recovered in this way needs to be separated beforethe purified oil can be returned to the tank.

An example of such a lubrication system for a turbomachine is describedin particular in document EP 0 513 957. That system presents numerousdrawbacks. In particular, it requires a large number of recovery pumpsto be used (one pump per enclosure), thereby increasing the weight ofthe turbomachine. It also requires a non-negligible quantity of air tobe taken from one of the compressors of the turbomachine in order topressurize the enclosures, and that is penalizing in terms of thespecific fuel consumption of the turbomachine. Finally, it consumes alarge amount of lubricating oil because the efficiency of de-oiling is adecreasing function of air flow rate.

U.S. Pat. No. 4,525,995 discloses a system for lubricating the frontenclosure of a turbomachine in which the oil/air mixture injected intothe enclosure flows into the accessory drive gearbox, which gearboxcontains at its outlet a recovery pump and an oil/air separator. Thatsystem also presents numerous drawbacks. In particular it requires apump to be present for recovering the oil/air mixture, therebyincreasing the weight of the turbomachine. Furthermore, that systemapplies only to the front enclosure of the turbomachine, with nothingbeing provided for lubricating other enclosures of the engine.

OBJECT AND SUMMARY OF THE INVENTION

A main object of the present invention is thus to mitigate suchdrawbacks by proposing a lubrication method that is simplified, light inweight, and consumes little oil or compressed air.

This object is achieved by a method of lubricating a turbomachinecomprising: at least two distinct enclosures closed at their ends by lowair flow rate seals, having low outlets and containing rolling bearingsfor supporting shafts; an oil tank; an oil feed pump; and an oil/airseparator, the method consisting, in accordance with the invention, ininjecting the oil from the tank into the enclosures by means of the pumpin order to lubricate the bearings; introducing compressed air at a lowflow rate into the enclosures through the seals in order to pressurizesaid enclosures; recuperating all of the air and the oil introduced intothe enclosures via their low outlet; using gravity and pressurization ofthe enclosures by the air introduced therein to convey the oil/airmixture as recovered in this way to the oil/air separator; separatingthe oil and the air of said mixture by means of the oil/air separator,the operation of the oil/air separator being controlled so as to betriggered only when oil is present at its inlet; returning the oil tothe tank; and exhausting the air to outside the turbomachine.

The use of gravity and the pressurization of the enclosures forrecovering all of the injected oil and oil makes it possible to avoidhaving recourse to recovery pumps such as those disclosed in the priorart. In addition, all of the oil and air injected into the enclosures isrecovered via a single common air and oil circuit, thereby avoidinghaving recourse to a special circuit for removing and de-oiling the airintroduced into the enclosures as described in the prior art. The methodof lubrication is thus lighter and simpler.

According to the invention, the method consists in controlling theoperation of the oil/air separator so as to operate it only when oil ispresent at its inlet. Controlling the oil/air separator thus makes itpossible to save power.

In an advantageous disposition, the method also consists in controllingthe operation of the oil feed pump to regulate the flow rate of oilconveyed to the enclosures as a function of the pressure and/or thetemperature inside the enclosures. For this purpose, the oil feed pumpmay be started only when the temperature inside the enclosures risesabove a given temperature. Controlling the pump makes it possible toavoid feeding the enclosures with oil when the oil/air mixture is nolonger being recovered by gravity.

Preferably, the method further consists in cooling the oil prior toconveying it to the enclosures.

The present invention also provides a turbomachine lubrication system,characterized in that it comprises at least two distinct enclosuresclosed at their ends by low air flow rate seals and housing rollingbearings for supporting shafts; an oil tank; an oil feed pump forfeeding the enclosures with lubricating oil from the tank; means forintroducing compressed air at a low flow rate into the enclosuresthrough the seals in order to pressurize them; means for recoveringunder gravity and under the effect of the enclosures being pressurized,all of the air and the lubricating oil introduced into the enclosures;an oil/air separator for separating the oil and the air of the mixture;means for controlling the operation of the oil/air separator; means forreturning the oil to the tank; and means for exhausting the air tooutside the turbomachine.

Preferably, the lubrication system further comprises means forcontrolling the operation of the oil feed pump.

According to another advantageous characteristic, the oil/air separatorincludes a pumping function to assist sucking the oil/air mixturerecovered from the enclosures and returning the oil to the tank.

According to yet another advantageous characteristic, the oil feed pumpand/or the oil/air separator are electrically driven.

The invention also provides a turbomachine including a lubricationsystem as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention appearfrom the description below made with reference to the accompanyingdrawings that show an embodiment having no limiting character. In thefigures:

FIG. 1 is a diagrammatic longitudinal section view of a turbomachineshowing the environment of the invention; and

FIG. 2 is a diagram showing the flow of oil and air in an aviationbypass turbomachine in application of the method of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 is a diagram showing a portion of an aviation bypass turbomachine2 in which the lubrication method and system of the invention can beimplanted. Naturally, the present invention applies to any other type ofturbomachine (single spool, triple spool, single-flow, industrial,etc.).

In well-known manner, the turbomachine 2 of longitudinal axis X-Xcomprises in particular a fan casing 4, a low-pressure spool 6, ahigh-pressure spool 8, a combustion chamber 10, and an accessory drivegearbox 12.

The low-pressure spool 6 comprises a low-pressure shaft 14 centered onthe longitudinal axis X-X, a fan 16 mounted at the front end of thelow-pressure shaft, a low-pressure compressor 18 fastened to the fan,downstream therefrom, and a low-pressure turbine 20 mounted on the rearend of the low-pressure shaft.

The high-pressure spool 8 comprises a high-pressure shaft 22 disposedconcentrically around the low-pressure shaft 14, a bevel gear 24 mountedat the front end of the high-pressure shaft, the high-pressurecompressor 26 mounted on the high-pressure shaft downstream from thegear 24, and a high-pressure turbine 28 mounted on the rear end of thehigh-pressure shaft.

For reasons of clarity, the various compressors and turbines of thehigh- and low-pressure spools of the turbomachine are represented inFIG. 1 as having blades in single stages. Naturally, and in well-knownmanner, these elements could have blades in several stages.

The accessory drive gearbox 12 comprises an angle transmission box 12 aand the accessory drive gearbox 12 b proper, these units being fastenedunder the fan casing 4, e.g. on a bottom face 4 a thereof. The accessorydrive gearbox 12 b is generally driven by the high-pressure shaft 22 viaan intermediate shaft 30 carrying a bevel gear 32 at its top end and abevel gear 34 at its bottom end.

In order to withstand the radial and axial loads, the low- andhigh-pressure shafts 14 and 22 of the turbomachine are supported byrolling bearings (ball bearings or roller bearings). Thus, thelow-pressure shaft 14 is supported at its front end by a front bearing36 a and at its rear end by a rear bearing 36 b. Similarly, thehigh-pressure shaft 22 is supported at its front end by a front bearing38 a and at its rear end by a rear bearing 38 b.

In order to reduce friction, wear, and heating, due in particular to thehigh speeds of rotation of the shafts of the turbomachine, the front andrear bearings 36 a & 38 a and 36 b & 38 b need to be lubricated bycontinuously injecting oil between the rings of these bearings viainjection nozzles (not shown in the figures).

In order to prevent the lubricating oil that is injected in this wayescaping from the turbomachine, the front bearings 36 a and 38 a and therear bearings 36 b and 38 b are confined in respective front and rearenclosures 40 a and 40 b. These enclosures 40 a and 40 b are distinctfrom each other and they are hermetically closed at their upstream anddownstream ends by annular seals 42 a, 42 b.

The seals 42 a, 42 b are leaktight with low air flow rates. For examplethey may be dynamic gaskets on cushions of air (also referred to ascarbon gaskets with lift). By way of example, reference can be made toEuropean patent application EP 1 055 848 which describes such gaskets.This type of gasket is particularly good at withstanding leaks, evenwhen the enclosures are at slightly raised pressures and theyessentially comprise labyrinth seals together with a static ring ofcarbon segments associated with a rotary surface having grooves forcreating lift.

Each enclosure 40 a, 40 b includes in its bottom (or low) portion aspecific outlet 44 a, 44 b enabling the oil/air mixture injected intothe enclosure to be recovered in a manner that is described below.

The method of lubricating such a turbomachine in accordance with theinvention is described below with reference in particular to FIG. 2,which is a highly diagrammatic representation of the oil and air flow inthe turbomachine described with reference to FIG. 1.

In FIG. 2, lines referenced O represent a flow of lubricating oil, linesreferenced A represent a flow of air, and lines referenced O/A representa flow of an oil/air mixture.

Still in FIG. 2, there can be seen in addition to certain elements ofFIG. 1, a lubricating oil tank 46, an oil feed pump 48 (e.g. of theelectrically driven type), an oil/air separator 50 (e.g. of theelectrically driven type), and an oil cooler device 52. In known manner,these elements are generally fastened under the turbojet, e.g. againstthe accessory drive gearbox 12. For reasons of clarity in FIG. 2, theseelements 46 to 52, the accessory drive gearbox 12, and the turbomachineare nevertheless shown as being spaced apart from one another.

The method of the invention consists in particular in injecting oil offrom the tank 46 into each of the enclosures 40 a and 40 b of theturbomachine by means of the feed pump 48, the oil being for lubricatingthe rolling bearings.

A flow of compressed air A is also introduced into the enclosures 40 aand 40 b via seals to pressurize these enclosures (this flow of airbeing taken for example from the high-pressure compressor of theturbomachine). Since the enclosures are closed by low air flow rateseals, it suffices to inject air at a low flow rate into the enclosuresin order to pressurize them.

All of the air and the oil as introduced in this way into the enclosures40 a and 40 b is then recovered via their low outlets 44 a and 44 b. Theoil/air mixture O/A is conveyed merely under gravity and under theeffect of the enclosures being under pressure to the oil/air separator50 that is situated below the enclosures.

In practice, the oil/air mixture O/A recovered from the front enclosure40 a can be taken to the oil/air separator by flowing along a removalpipe (not shown in the figures) that runs parallel to the intermediateshaft 30 for driving the accessory drive gearbox 12 and leading to theseparator.

Likewise, the oil/air mixture O/A recovered from the rear enclosure 40 bcan be conveyed to the oil/air separator by flowing along anotherremoval pipe (not shown in the figures) that is incorporated in an armof the turbomachine structure and that opens out into the separator.

Recovery of all of the oil/air mixture by gravity and under the effectof the enclosures being pressurized is made possible in particular bythe fact that the pressure inside the enclosures is greater than thepressure in the separator and the separator is situated lower than theenclosures.

The oil/air mixture O/A is introduced into the separator 50 in order toseparate the oil from the air, the purified oil then being returned tothe tank 46. An oil cooler device 52 located downstream from the pump 48serves to cool the purified oil (alternatively, the oil cooler devicecould be interposed between the separator 50 and the tank 46). The airthat is recovered at the outlet from the separator is exhausted tooutside the turbomachine.

The oil/air separator 50 may be of the dynamic type, i.e. operating onthe principle of dynamically centrifuging the oil/air mixture in orderto recover the oil and the air separately. Alternatively, the oil/airseparator could be of the static type.

The oil/air separator 50 may incorporate a pumping function to assist insucking in the oil/air mixture O/A recovered from the bottom portions ofthe enclosures and in order to deliver purified oil to the tank. Such afunction may be made necessary if the pressure in the enclosures is toosmall or if the tank 46 is at an unsuitable height relative to theseparator 50.

In an advantageous disposition of the invention, provision is made tocontrol the operation of the oil/air separator 50 so as to trigger suchoperation only when oil is present at its inlet. For this purpose, anoil presence detector 50 a can be mounted at the inlet to the separatorand coupled to its electrical power supply (when the separator is of theelectrically driven type).

The oil/air separator can be controlled because it is electricallydriven and thus powered independently of the speed of operation of theturbomachine. By means of such control, it is possible to guarantee thatthe oil/air mixture is removed from the enclosures and that purified oilis returned to the tank regardless of the operating speed of theturbomachine. Controlling the separator also makes it possible to savepower when the separator is not powered continuously.

In another advantageous disposition of the invention, provision can alsobe made to control the operation of the oil feed pump 48 to regulate theflow rate of oil delivered to the enclosures as a function of thepressure and the temperature inside the enclosures. Controlling the pumpmakes it possible to avoid feeding oil to the enclosures when theoil/air mixture is no longer being recovered by gravity.

In practice, the operation of the oil feed pump can be controlled bystarting the pump directly on the basis of the oil pressure measuredinside the enclosures. Alternatively, the pump may be triggered solelyabove a given temperature inside the enclosures (sensed by appropriatemeasurement devices).

It should be observed that the oil feed pump may be controlledindependently of or together with the above-described control of theoil/air separator.

It is also possible to observe that the lubrication method as describedabove can also be applied to lubricating the gearing of the accessorydrive gearbox 12.

As shown in FIG. 2, the lubricating oil of from the tank 46 is injectedvia a feed pump 48 into the angle transmission box 12 a and theaccessory drive gearbox 12 b proper. In addition, a flow of air A takenfrom the front enclosure 40 a is taken to these units 12 a and 12 b inorder to pressurize them. After lubricating the gearing in the unit 12 aand 12 b, the oil flows to a low point thereof. Under the effect ofthese units being pressurized, the oil/air mixture that is formed isthen discharged via a low outlet 54 to be conveyed to the inlet of theoil/air separator 50 and thus return to the lubrication circuit of theturbomachine.

1-9. (canceled)
 10. A method of lubricating a turbomachine including atleast two distinct enclosures closed at their ends by low air flow rateseals, low outlets and containing rolling bearings for supportingshafts, an oil tank, an oil feed pump, and an oil/air separator, themethod comprising: injecting oil from the tank into the enclosures bythe oil feed pump to lubricate the bearings; introducing compressed airat a low flow rate into the enclosures through the seals to pressurizethe enclosures; recuperating all of the air and the oil introduced intothe enclosures via their low outlet; using gravity and pressurization ofthe enclosures by the air introduced therein to convey the oil/airmixture as recovered in this way to the oil/air separator; separatingthe oil and the air of the mixture by the oil/air separator, operationof the oil/air separator being controlled so as to be triggered onlywhen oil is present at its inlet; returning the oil to the tank; andexhausting the air to outside the turbomachine.
 11. A method accordingto claim 10, further comprising controlling operation of the oil feedpump to regulate the flow rate of oil conveyed to the enclosures as afunction of pressure and/or temperature inside the enclosures.
 12. Amethod according to claim 11, wherein the oil feed pump is started onlywhen the temperature inside the enclosures rises above a giventemperature.
 13. A method according to claim 10, further comprisingcooling the oil prior to conveying the oil to the enclosures.
 14. Aturbomachine lubrication system comprising: at least two distinctenclosures closed at their ends by low air flow rate seals and housingrolling bearings for supporting shafts; an oil tank; an oil feed pumpfor feeding the enclosures with lubricating oil from the tank; means forintroducing compressed air at a low flow rate into the enclosuresthrough the seals to pressurize the enclosures; means for recovering,under gravity and under effect of the enclosures being pressurized, allof the air and the lubricating oil introduced into the enclosures; anoil/air separator for separating the oil and the air of the mixture;means for controlling the operation of the oil/air separator; means forreturning the oil to the tank; and means for exhausting the air tooutside the turbomachine.
 15. A system according to claim 14, furthercomprising means for controlling operation of the oil feed pump.
 16. Asystem according to claim 14, wherein the oil/air separator includes apumping function to assist sucking the oil/air mixture recovered fromthe enclosures and returning the oil to the tank.
 17. A system accordingto claim 14, wherein the oil feed pump and/or the oil/air separator areelectrically driven.
 18. A turbomachine, comprising a lubrication systemaccording to claim 14.